Childhood obesity is highly prevalent, spares no age group, and disproportionately affects racial/ethnic minority populations. Obesity in childhood is associated with adverse cardio-metabolic outcomes including hyperinsulinemia and insulin resistance which may, in turn, increase risks for many cancers. The lifecourse approach to chronic disease prevention posits that the right infiuences during infancy and early childhood could entrain healthful trajectories of weight and energy balance for life. Mounting epidemiologic evidence indicates that short duration of sleep is a risk factor for obesity, insulin resistance, coronary heart disease, and all-cause mortality in adults independent of other risk factors. In addition, short-term experimental studies show that sleep restriction in adults is associated with physiologic mechanisms that may increase risk of adiposity and cardio-metabolic disorders. Yet major questions remain regarding the extent to which short sleep duration predicts adiposity and cardio-metabolic disorders in young children, and the potential mechanisms underiying these associafions. Furthermore, few studies have examined the social-environmental context of early childhood sleep patterns that could inform behavioral intervenfions to improve sleep in high-risk groups. The goals of this study are two-fold. The first goal is to examine associafions of sleep duration - a novel risk factor for obesity and metabolic dysfunction identified in the first wave of TREC projects - in infancy and childhood with adiposity and energy balance, and with the emergence of insulin resistance and other cancer related biomarkers in eariy adolescence. We will carry out this part ofthe project within the well-characterized pre-birth cohort study. Project Viva. This US-based study has prospecfively collected and validated sleep and diet information, anthropometry, and research-quality biomarker data in children from eariy infancy through age 11 years. The second goal is to examine the social-cultural, behavioral, and environmental context of early childhood sleep patterns that could inform behavioral interventions to improve sleep duration and quality. To achieve our aims, we have assembled a transdisciplinary research team of obesity and sleep medicine epidemiologists, behavioral scientists, clinical psychologists, pediatric clinical investigators, statisticians, and geneticists. The results of this study could strengthen the understanding of sleep, energy balance, and carcinogenesis from micro- (genetics) to macro- (environment) levels among children - a segment of the population at high risk for obesity and its sequelae. Furthermore, our study will supply key data needed for the design of future intervention studies, such as quantifying threshold levels of sleep that confer increased risk of obesity and metabolic dysfunction, identifying key proximate behaviors that mediate these associations, and identifying socio-cultural/environmental factors as potential targets for sleep improvement interventions.